[PATCH RFC] SUNRPC: Fail quickly when server does not recognize TLS

[Chuck Lever <cel@xxxxxxxxxx>]

From: Chuck Lever <chuck.lever@xxxxxxxxxx>

rpcauth_checkverf() should return a distinct error code when the
server does not recognize the AUTH_TLS probe so that the client's
header decoder can respond appropriately.

Suggested-by: Trond Myklebust <trondmy@xxxxxxxxxxxxxxx>
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
 net/sunrpc/auth.c     |   11 ++++++++---
 net/sunrpc/auth_tls.c |    2 +-
 net/sunrpc/clnt.c     |   10 +++++++++-
 3 files changed, 18 insertions(+), 5 deletions(-)

Compile-tested only, but something like this should be adequate.

diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c
index 2f16f9d17966..814b0169f972 100644
--- a/net/sunrpc/auth.c
+++ b/net/sunrpc/auth.c
@@ -769,9 +769,14 @@ int rpcauth_wrap_req(struct rpc_task *task, struct xdr_stream *xdr)
  * @task: controlling RPC task
  * @xdr: xdr_stream containing RPC Reply header
  *
- * On success, @xdr is updated to point past the verifier and
- * zero is returned. Otherwise, @xdr is in an undefined state
- * and a negative errno is returned.
+ * Return values:
+ *   %0: Verifier is valid. @xdr now points past the verifier.
+ *   %-EIO: Verifier is corrupted or message ended early.
+ *   %-EACCES: Verifier is intact but not valid.
+ *   %-EPROTONOSUPPORT: Server does not support the requested auth type.
+ *
+ * When a negative errno is returned, @xdr is left in an undefined
+ * state.
  */
 int
 rpcauth_checkverf(struct rpc_task *task, struct xdr_stream *xdr)
diff --git a/net/sunrpc/auth_tls.c b/net/sunrpc/auth_tls.c
index de7678f8a23d..751b3f418f3b 100644
--- a/net/sunrpc/auth_tls.c
+++ b/net/sunrpc/auth_tls.c
@@ -131,7 +131,7 @@ static int tls_validate(struct rpc_task *task, struct xdr_stream *xdr)
 	if (xdr_stream_decode_opaque_inline(xdr, &str, starttls_len) != starttls_len)
 		return -EIO;
 	if (memcmp(str, starttls_token, starttls_len))
-		return -EIO;
+		return -EPROTONOSUPPORT;
 	return 0;
 }
 
diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 315bd59dea05..80ee97fb0bf2 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -2722,7 +2722,15 @@ rpc_decode_header(struct rpc_task *task, struct xdr_stream *xdr)
 
 out_verifier:
 	trace_rpc_bad_verifier(task);
-	goto out_garbage;
+	switch (error) {
+	case -EPROTONOSUPPORT:
+		goto out_err;
+	case -EACCES:
+		/* Re-encode with a fresh cred */
+		fallthrough;
+	default:
+		goto out_garbage;
+	}
 
 out_msg_denied:
 	error = -EACCES;